Systems and methods herein generally relate to security printing and more particularly to systems, devices, and methods that produce an apparent color shift region within a document.
In the area of security printing, documents are protected from copying, forging, and counterfeiting using multiple techniques. Some methods of security printing use standard materials such as papers, inks, and toners; however, more typically security printing requires special and expensive materials. Example documents needing security printing include legal documents, negotiable documents, prescriptions, etc., where a user would like to be able to have a high level of confidence that the document is genuine.
For example, color shifting ink appears as one color from a certain angle and another color from another angle. However, such color shifting printing requires a very specialized ink, that can be regulated and/or expensive. Many US currency denominations use regulated color-shifting ink to print the numerals located in the corners on the front of the bill. One example of color shifting printing is on a US twenty dollar bill at the bottom right corner where the number 20 appears gold or green depending on how the bill is tilted. Similarly, on a genuine $100 banknote, the green color will “shift” to grey and back to green as you tilt the bill back and forth to change the viewing angle (and the $100 bill available October 2013 goes from copper to green).
The “optically variable ink,” as it is officially called, used to print currency is not widely commercially available. Most of it comes from a Swiss manufacturer (SCIPA), which grants the U.S. exclusive rights to the green-and-black ink used for printing dollars. One feature of optically variable ink is that such ink cannot be replicated by copiers, because copiers only “see” and replicate patterns from a fixed angle.
Some printing techniques enable printing small overt security features that could not easily be copied by a digital copier, if at all. However documents protected with such features can potentially be reproduced with reverse engineering.